Cartridge-type fuses have been heretofore designed which provide an indication of an open fuse condition with the deposition of a visible coating on the inside surfaces of the transparent fuse housings. One such fuse is disclosed in U.S. Pat. No. 4,603,315, assigned to the owner of the present patent application. The fuse utilizes a two component pyrotechnic mixture which produces a colored smoke when ignited. Except for this patented fuse, prior art indicating fuses did not provide evidence of current overloads or transients which may not be of sufficient magnitude or duration to initiate operation of the fuse. This prior art patented fuse was not commercially produced because of manufacturing difficulties, cost considerations, and the hazardous nature of the pyrotechnic coating materials involved.
Indicating fuses have also been heretofore developed which provide by mechanical means an indication of an open fuse condition. The cost of manufacture of such fuses makes them impractical for use as replacements for commonly used low-cost fuses.
It would be highly advantageous to provide an economically manufacturable fuse from non-hazardous materials which would be capable of producing visual evidence of electrical loading conditions (1) sufficient to cause fuse element disruption, (2) approaching circuit overload levels for a significant time interval, and (3) exceeding overload conditions but for a time period insufficient to produce opening of the fuse. The occurrence of an indication from either of the latter circuit conditions would enable responsible parties to investigate the electrical equipment system, determine the source of the excessive current, and initiate corrective actions before possible nuisance service interruption or actual damage to circuit components might take place.